Oral N-acetylcysteine (NAC) exerts a beneficial action in chronic bronchitis by reducing the number of exacerbations. There have been few studies of the effect of NAC (or of any other drug) on general well-being in chronic bronchitis. We used an established psychiatric instrument (General Health Questionnaire; GHQ) and a visual analogue scale (VAS) to measure well-being in a 22-week, placebo-controlled, double-blind, parallel-group study of NAC administered as sustained release tablets 600 mg b.i.d., including during the winter months, to patients with mild chronic bronchitis. One hundred and fifty-three patients were accepted for randomized treatment, 129 finished the study (59 NAC, 70 placebo), and well-being was measured in 105 (46 NAC, 59 placebo). The number of observed exacerbations was unexpectedly low in both groups. The number was lowest in the NAC group, however, the difference did not reach statistical significance in the present study (P = 0.08). There were no statistically significant differences between NAC and placebo in subjective symptom scores, FEV1 or FVC. The distribution of GHQ score at baseline was uneven, but NAC was significantly superior to placebo in terms of a favourable effect on GHQ score. GHQ score correlated with the number of exacerbations, and VAS correlated with GHQ score. This study therefore demonstrates the validity of measuring general well-being in patients with mild chronic bronchitis. Future studies of the treatment of chronic bronchitis should use a battery of more specifically adapted instruments which are now becoming available to measure well-being.